The invention relates to a shifting device for a multi-speed hub.
German Patent DE 42 29 023 disclose a multi-speed hub which has a shifting device between two locking-mechanism levels in a multi-speed hub which can be shifted backward and forward even under load. The shifting is achieved by propulsion pawls which are held forcibly in driving engagement, are arranged one above the other and have an angle of tooth engagement chosen such that the propulsion pawls slide out of engagement under load. A control disk can be displaced under the propulsion pawls, thereby alternately holding the pawls fast and locking them in their associated ratchet toothing. The control disk is taken along at the driving speed by means of a driver disk in the pawl carrier and has a rearward rotational idle travel relative to the propulsion pawls which is necessary in order to use the initial angular degrees when braking by backpedaling to lift out the forcibly held propulsion pawls. Such a shift mechanism has the advantage, by virtue of the division of the power transmitted into a driving component and an inward-directed control component, of only requiring the management of the smaller control component, even under load.
The present invention is in a greatly simplified and low-cost shift unit for a multi-speed hud which can likewise disengage the pawls of the pawl-controlled hub under load and maintain them in this disengaged state.
The invention is formed with a shift sleeve, which is arranged around a hub axle, and a shift bushing connected rotatably to it, the sleeve and the bushing having on their respective end faces shift projections which are separated by gaps of sufficient width to slide under the respective pawl to be lifted out. The pawl is enclosed on both sides by projections. Since the shift sleeve and the shift bushing each have a different and, in particular, slower rotational speed than the pawls, a projection which has slid in front of the pawl will slide under the latter due to the propulsive power of the driving torque from the rider and will lift out the pawl. The control force required for the above described shift operation is not particularly great but it must be considered that the profiles do not always approach the respective pawls in the desired manner. If a projection collides with a pawl, the latter cannot be lifted out by the projection if the applied torque is high. Only if the pawl is between two projections can the projection slide under the pawl and disengage the latter from its torque connection. However, the projection can lift the pawl out even when this pawl is not transmitting any significant torque. This advantage in terms of shifting, which is also present to allow shifting through the gear ratios when the transmission is stationary, is provided by additional bevels on the pawl. It is furthermore proposed to enhance the capability for shifting through the gears by arranging conical chamfers on the end faces of the projections and/or the gaps between the projections in addition to the bevels on the pawls, the alignment of the chamfers coinciding approximately with the bevels on the pawls. Finally, the projections of the profile on the shift bushing and on the shift sleeve have bevels which are arranged in the circumferential direction and which can act as a load-limiting means by virtue of the fact that the shift bushing or the shift sleeve is repelled by the pawls when large torques are being transmitted via the pawls. It is advantageous to connect the shift bushing and/or the shift sleeve to a rider-operated remote control by means of storage springs which allows a change in gear ratio only when a certain lift-out torque is reached and which delay the shift operation. It is possible, by means of the configuration of these storage springs, to define the desired lift-out torque, thereby avoiding excessive shifting shocks. The shift sleeve or the shift bushing will thus find another location for engagement under the pawl, which will be lifted out when the torque is reduced.
In a three-speed hub, a first pawl is mounted on the annulus and engages the toothing of the hub sleeve. Since the annulus necessarily rotates more rapidly than the planet carrier when the latter is being driven, it is necessary to couple the shift bushing to a coupling ring rotating at the rotational speed of the planet carrier. On the other hand, the shift bushing must be axially displaceable, something which can only be achieved by means of a shift component, which preferably is a thrust block connected to a remote control. The two movements described above can be imparted to the shift bushing on the one hand by virtue of the rotatable mounting of the shift bushing on the shift sleeve, which is connected in a rotationally rigid manner to the thrust block, and secondly by virtue of the mounting of the shift bushing in a slot in the coupling ring, which rotates more slowly when a fast gear has been selected than the pawl operatively connected to the hub sleeve.
If the connection between the driver and the planet carrier is likewise by way of a pawl, what has been stated above applies in as much as the pawl of the more slowly rotating planet carrier overtakes the profile of the shift sleeve, which is connected in a rotationally rigid manner to the hub axle but is axially displaceable, and provides the same lift-out conditions for the pawl as those described above in connection with the shift sleeve. To ensure operation during backpedaling, the pawls in the region of the foot, should have a contour such as a rounding or chamfer so that the pawls are lifted out and do not jam in the event that they have not yet been lifted out but are still in the region between the projections. Since there is no load on the pawls during backpedaling, the only point of importance is that the rounding should be sufficiently great.
Finally, it is advantageous not to maintain the shift bushing in an axially fixed position on the shift sleeve but to hold it by means of a storage spring since there, as described, brief hindrances to shifting have to be compensated for if it is required to be able to operate the remote control without resistance.
The object of the invention is therefore to provide a shifting device for a multi-speed hub which can perform the gear change while stationary and even under load without a significant increase in the control forces on a remote control.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.